HPLC--residue analysis of the herbicide pyridate in cereals

For many reasons residue analysis of plant protecting chemicals is becoming of increasing importance. The demand of modern trace analysis techniques is to detect significantly and sensitively values down to levels in the ppb range or even less. Aggravating circumstances are the complex multicomponent sample matrices out of whom the residue analysis has to be performed; theoretically thousands of compounds could be present and interferences with substances of interest are quite likely. One way to get around these difficulties is to employ multidimensional HPLC (MD-HPLC). A method using this invaluable analytical tool tracing Pyridate and its main metabolites in various plant extracts is presented. Based on a brief discussion about requirements of modern trace analysis HPLC in connection with column switching we designed an automatizable setup combining a weak anionexchanger (dimethylamine phase) with a reversed phase system handling relatively large aqueous sample volumes. Depending on specifically described sample pretreatment schemes detection limits down to 30 ppb are routinely obtained. At this level acceptable on-line UV-spectra can be obtained via inserting a spectrophotometric detector in a loop of a 6-port valve. The usefulness of the method described has been demonstrated by analysing several hundred samples.